Am I supposed to kill him?
Its 6 lvl 15 enemies vs 4 LvL 13!

Ive done the quests that leads up to discover that waterfall...
I gotta say... most of the game feels terrible. A lot of the quest just says "We dont know where to get the information to proceed." And there seems to be a weird way to go about battles.

Most battles are 4 of you vs 6-7 Overpowering individuals.

Many people like a challange and feel that an easy game is a bad game.

You don't have to, unless you have a certain companion. That companion can also make the combat *harder* under certain circumstances. Even with the companion, it is optional - you can completely avoid that cave - some character development is missed, though. As is usually the case, coming back later is a good option if you want the experience but don't feel up to the fight quite yet.